Materials often exhibit a variety of different failure mechanisms. On occasion, materials are loaded beyond a tensile strength of the material and the material fractures abruptly and completely. In these circumstances the material is usually irreparable and must be replaced. However, often materials do not fall in an abrupt complete manner, but rather fail due to fatigue or localized stresses which exceed design criteria, causing cracks to form in the material. Often when these cracks initially form, the material is still functional for its desired purpose. For instance, a reciprocating machine may receive cracks in its structural material and yet continue to operate, albeit at perhaps a lesser efficiency. Cracks thus serve as indicators that a material is being over stressed and yet also provide an opportunity for remedial measures to be taken without requiring entire replacement of the affected materials.
While crack repair methods have become well known in the art, they have traditionally been looked upon as primarily a temporary or stopgap measure which usually cannot be relied upon to permanently repair a crack-damaged material. Usually "repaired" cracks are still weaker than surrounding material and thus are subject to recracking or other failure in the same location. However, crack repair is attractive in that it can often extend the life of the material without requiring significant downtime for the machinery which utilizes the material. Thus, crack repair can result in the avoidance of significant replacement costs.
Accordingly, a need exists for a method and apparatus for crack repair which can be performed in a low-cost, timely manner and yet repair the crack to a level which makes the material as strong as (or stronger than) it was before the crack occurred.
Crack repair pins or "plugs" have been known in the art which are threaded into holes drilled in the cracks to prevent cracks from continuing to propagate. These "plugs" have also been somewhat effective in resealing materials such as cast iron casings which require that they maintain a somewhat pressurized environment without allowing fluids to escape therefrom.
In addition, locks are known in the art which can draw cracks together somewhat and extend the life of a material which is cracked.
However, neither of these solutions can effectively strengthen the material to a level which makes it stronger than it was before the crack occurred and also effectively seal up the crack to establish a pressure-withstanding seam. The device of this invention, when used in accordance with the method of this invention, includes pins which have threads that angle upward toward the head of the pin. These upwardly angled threads engage with complementally formed threads in holes drilled into the crack. When the pins are advanced into the crack, the upwardly sloped threads draw opposite sides of the crack toward each other. Thus, the crack is actually drawn closed and sealed by the pins located within the crack.
Various devices are known in the art which include threads which extend upwardly. However, none of these threaded devices are configured to include all of the features of the pins of this invention. Furthermore, none of the threaded devices having upwardly sloping threads have been utilized in conjunction with a method for sealing cracks within a material.